This invention pertains to down hole drilling equipment utilizing down hole drilling motors for straight and directional drilling. More particularly it relates to apparatus to be attached to the drilling motor body and motor output shaft, as an extension of the drilling motor, for selectively deflecting the rotational centerline of a drill head.
Directional drilling utilizing down hole motors is an established art with many forms of apparatus, for attachment to motors, designed for particular purposes. Particular needs relate to the ability to choose the configuration of the down hole assembly to drill straight ahead or laterally deflect the drill head, for directional drilling, without loss of time in tripping the drill string. Ideally, the configuration change should result from the selective manipulation of an existing influence such as drilling fluid flow rate. Down link controls by such means as electrical conductors inside the drill string have been used but that imposes an additional burden on the drilling operation. Objects such a balls and spears have been dropped down the drill string bore to cooperate with receiving contrivances down hole to cause desired changes in the behavior of the down hole assembly. Again, that activity utilizes equipment and actions not already essential to drilling. The mud pumps and controls are essential to drilling. Their use, in manipulating down hole apparatus, introduces nothing new to the system and the required manipulations of the flow rate can be carried out with the mud pump throttle. Such down link command systems are in current use in several forms and are preferred for control of the present invention.
The apparatus is part of a length of drill string that includes a down hole drilling motor. A drill head normally completes the assembly and is attached to the output shaft of the apparatus. Drilling fluid flows down the drill string, through the drilling motor, the apparatus and, finally, out the ports of the drill head. A housing to contain the apparatus is attached to the body of the drilling motor. The apparatus has a flexible drive shaft, or arbor, that drives the drill head, is bearingly supported in the housing, and is attached to the drilling motor output shaft at the upper end and the drill head at the lower end. The motor output shaft is axially and radially supported within the motor, hence, it is axially and radially fixed relative to the apparatus housing. The arbor consists essentially of three major, flexibly connected and rotationally connected segments. The upper segment is mounted on the motor shaft and rotates about a fixed centerline and has a spline connected lower portion that is axially movable to extend it""s length. The center segment is gimbal connected to the lower end of the upper segment and upper end of the lower segment. The center segment moves rotationally and can be displaced axially within the housing. The center segment has a mid-length laterally deflecting arrangement that causes it to move laterally when it is moved axially. With the upper segment radially supported on the apparatus centerline, that deflection causes the lower end of the center segment to move a greater amount laterally. The lower end of the center segment is gimbal connected to the upper end of the lower segment which pivots about a hinge point on the housing to cause it""s lower end to deflect. That lower end carries the drill head. Deflection of the drill head relative to the housing, and the well bore, causes the overall assembly to drill an advancing hole being drilled that departs from the original well bore centerline. The hinge point is in a ball arrangement that is mounted in a bearing assembly in the housing. It is axially fixed but rotates relative to the housing and is rotationally and axially secured to the lower segment. The lower segment has an upper end that telescopes to accept the axial movement of the center segment. It is spring loaded to urge the center segment upward.
A flow bore extends through the arbor to receive mud from the motor shaft and deliver it to the drill head.
The center segment is deflected by a camming sleeve, mounted for rotation relative to the segment and axially affixed thereto. The sleeve slides along a bore in the housing when the center segment moves axially. Axial movement of the sleeve, in cooperation with cam surfaces on the bore, pushes the center segment laterally.
Axial movement of the arbor is confined to the lower end of the upper segment, all of the center segment, and the upper end of the lower segment. The axial movement is powered by drilling fluid pressure acting on a piston surface in the upper segment, with the reference pressure existing in the general enclosure of the housing. The general enclosure pressure is defined by a vent from the flow bore to the enclosure of the housing.
A selector valve is situated in the flow bore within the center segment and, when closed, causes a pressure difference between the upper and lower reaches of the flow bore that extends through all three segments. The pressure in the flow bore above the closed valve is greater than that below the valve, and the flow bore below the valve is vented to the housing general enclosure, and that pressure difference actuates the piston. When the valve is open the pressure difference on the actuator piston is caused only by flow related pressure loss in the flow bore between the piston and the point of venting to the enclosure.
To insure that the deflecting means responds only to a closed selector valve the camming sleeve has optional sealing surface, or seal ring, that cooperate with sealing surfaces on the housing to fluidly separate the enclosure into upper and lower chambers. The chambers are sealingly separated only in the non-deflected state. The flow bore vent is below the camming sleeve. When the apparatus is in the straight drilling configuration, the pressure difference across the camming sleeve produces an upwardly directed piston force. That force cancels the tendency for flow losses in the flow bore to actuate the deflecting piston when the selector valve is open.
Further steps to prevent inadvertent deflection include an optional controlled vent from the enclosure above the camming sleeve through the housing wall to drain pressure at a limited rate from the upper chamber to the well bore. The vent speeds up the arbor straightening action when the selector valve is opened. That vent also accepts some leakage from the flow bore or motor drive shaft seal above the sleeve without producing a downward force on the camming sleeve, and prevents lock up when the seal ring is being extracted from the cooperating sealing surface for downward movement. The controlled vent is small compared to the vent in the flow bore. When the sleeve moves away from the sealing position the vent in the flow bore effectively defines the pressure in the general enclosure.
It is therefore an object of this invention to provide apparatus attachable to a drilling motor to change the apparatus between a straight hole drilling configuration a directional drilling configuration in response to signals received from the surface.
It is another object to provide apparatus that responds to manipulations of the drilling fluid flow rate, generated at the surface, to change the configuration of the apparatus during brief interruptions in the drilling activity.
It is yet another object to provide intrinsic compensation to prevent the apparatus from responding to high flow rate pressure losses in the apparatus from shifting unintentionally to the directional configuration.
These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from a consideration of this specification, including the attached claims and appended drawings.